- Rh is one of the important blood group system and D antigen is the most immunogenic and clinically significant because of the ability to cause haemolytic disease of new born and transfusion reactions. The monoclonal anti-D reagents used to detect D antigen vary widely in their ability to detect both partial and weak D but can detect the weakest Rh D type. Variation of clones used in the monoclonal anti- D reagent may cause discrepancies when variant D is detected. Recently as part of our cost saving measure we introduced the use of DiaClon ABD (DVI-) confirmatory cards for patients with a known historical blood type but the different clone of monoclonal anti-D reagent used in the confirmatory card led to significant discrepancies between the historical and current RhD type on weak RhD patients. In order to assess the level of discrepancy on weak RhD patients a prospective audit was carried out from 01.11.2013 to 30.04.2014 on all samples that were reported RhD weak positive and on samples that did not match the historical RhD type. All antenatal samples which gave a weak reaction were referred to NHSBT for confirmation. 23 samples were identified to have weak RhD type and out of the 23 samples 3 did not have previous history therefore it was excluded from the study. Out of the 20 samples 6 (30%) gave a discrepant RhD type. Four of them gave RhD positive result and 2 of them Rh D Negative results. The samples which gave a negative result were referred to NHSBT and confirmed as Weak RhD type. Conclusion: Our audit shows significant discrepancies between the monoclonal reagents used and highlights the need for manufacturers to standardise the monoclonal reagents to minimise the weak RhD type discrepancies.